Fig. 7. Sources of RA and essential target tissues for RA signaling during optic cup formation. (A-E) RARE-lacZ expression in unrescued Raldh1^-/-;Raldh3^-/- embryos. (F-K) Raldh2 expression in wild-type embryos. (L-P) RARE-lacZ expression in limited-rescue Raldh1^-/-;Raldh2^-/- embryos. (Q-U) Raldh3 expression in wild-type embryos. (V-X) RARE-lacZ expression in limited-rescue Raldh2^-/-;Raldh3^-/- embryos. (Y) Raldh1 expression in a wild-type embryo. In all panels, dorsal is at the top and ventral at the bottom, and sections are frontal except for J, which is a horizontal section that has temporal at the top and nasal at the bottom. Embryo stages are indicated on each panel. D, dorsal; f, forebrain; le, lens; nr, neural retina; ov, optic vesicle; pm, perioptic mesenchyme; res, limited rescue (maternal RA from E6.75-E8.5); rpe, retinal pigment epithelium; se, surface ectoderm; tm, temporal mesenchyme; V, ventral.